The present invention relates to a derived electrocardiogram generating system and a derived electrocardiogram generating method which can improve accuracy in diagnosis of heart disease of a subject even with a small number of electrocardiographically measuring electrodes so as to achieve higher derivation accuracy than any existing technique.
To acquire a standard 12-lead electrocardiogram of a patient, 10 electrodes connected to an electrocardiograph are used so as to be mounted at six places for measuring chest leads and at four places for measuring limb leads respectively. Based on electrocardiographic potentials detected from the 10 electrodes, six limb lead waveforms (I, II, III, aVR, aVL and aVF) of standard 12-lead waveforms and six chest lead waveforms (V1, V2, V3, V4, V5 and V6) of the standard 12-lead waveforms are calculated and outputted by the electrocardiograph.
The following relations are established between lead waveforms for obtaining a standard 12-lead electrocardiogram and electrocardiographic potentials in measurement portions.
I lead: vL−vR
II lead: vF−vR
III lead: vF−vL
aVR lead: vR−(vL+vF)/2
aVL lead: vL−(vR+vF)/2
aVF lead: vF−(vL+vR)/2
V1 lead: v1−(vR+vL+vF)/3
V2 lead: v2−(vR+vL+vF)/3
V3 lead: v3−(vR+vL+vF)/3
V4 lead: v4−(vR+vL+vF)/3
V5 lead: v5−(vR+vL+vF)/3
V6 lead: v6−(vR+vL+vF)/3
where each sign v represents a potential detected in each electrode mounting position.
When heart disease of a patient is diagnosed with a large number of electrodes in this manner in a fully-equipped hospital or the like, the diagnosis can be performed in the condition that the patient is kept quiet in bed.
However, for example, in the case of home care or emergent care, it is often difficult to use a large number of electrodes and mount the electrodes in proper positions on a body surface of a living body respectively, in view of patient's condition. Further, it may be also difficult to transmit multi-channel signals in order to obtain a large number of lead waveforms. In such a case, there is only one channel (one lead) where a signal of an electrocardiogram can be transmitted. Thus, some lead waveforms of standard 12-lead waveforms are measured with no more than 2 to 4 electrodes, so as to diagnose heart disease.
From this view point, the present inventor has developed a derived 12-lead electrocardiogram constructing system and an electrocardiographic inspection apparatus for reconstructing a standard 12-lead electrocardiogram with which various heart diseases can be diagnosed and treated properly, by use of a lead system subset consisting of a minimum number of leads for obtaining a related-art standard 12-lead electrocardiogram (see JP-A-2002-34943, particularly paragraphs 0020-0033).
That is, in the system for constructing a derived 12-lead electrocardiogram as disclosed in JP-A-2002-34943, limb leads I and II and two chest leads V1 and V5 or V6 for obtaining the standard 12-lead electrocardiogram are used as a lead system subset consisting of a minimum number of channels. From these leads, leads III and aVs (aVR, aVL and aVF) are arithmetically obtained based on the aforementioned specific relations of the respective leads. In addition, the other chest leads V2, V3, V4 and V6 or V5 are arithmetically derived using conversion coefficients (deriving matrix) created in consideration of relationship among potentials, lead vectors and cardiac vectors.
Since a related-art lead system subset of a standard 12-lead electrocardiogram is used, a derived 12-lead electrocardiogram is obtained thus from the specific relations of the respective leads and the created conversion coefficients. Thus, electrodes can be easily and surely positioned in predetermined portions respectively when the electrodes are attached thereto. This work does not require much skill. In addition, a high-accuracy standard 12-lead electrocardiogram can be reconstructed. Thus, various heart diseases can be diagnosed and treated properly.
Accordingly, the related-art electrocardiograph can check and diagnose abnormality in electrocardiographic waveforms not only when a standard 12-lead electrocardiogram is obtained from six limb leads and six chest leads using ten electrodes but also when a high-accuracy derived 12-lead electrocardiogram is derived by the system disclosed in JP-A-2002-34943.
Another case where a derived electrocardiogram is required with respect to standard 12-lead applications will be described. With the aforementioned standard 12-lead electrocardiogram, which is applied to diagnosis of myocardial infarction, abnormality in electrocardiographic waveforms can be checked and diagnosed easily about an anterior wall or a side wall where a coronary artery providing a blood flow for a cardiac muscle is occluded. However, sensitivity deteriorates about a posterior wall or a right posterior wall where an electrode is attached in a farther position from the heart. According to research paper, ST increase of acute myocardial infarction (AMI) in many posterior walls appears in the leads V7, V8 and V9. Thus, ST increase may be often overlooked in a standard 12-lead electrocardiogram. It has been therefore proposed to measure the aforementioned additional leads if necessary. However, measurement must be carried out twice when a standard electrocardiograph is used. In addition, it is difficult to measure the leads V7, V8 and V9 because the leads V7, V8 and V9 are located on the back. Thus, the present inventor has proposed an electrocardiograph with an additional lead function and an additional lead electrocardiogram deriving method in which electrocardiographic waveforms V7, V8 and V9 for diagnosis of inferior infarction and electrocardiographic waveforms V3R, V4R and V5R for diagnosis of right ventricle infarction are derived from measured signals of a standard 12-lead electrocardiogram so that high-accuracy diagnosis information can be provided (see Japanese Patent No. 4153950).
According to the related-art electrocardiogram deriving method (e.g. Japanese Patent No. 4153950), electrocardiographic waveforms in portions to which electrodes are not attached, that is, derived electrocardiographic waveforms are derived using conversion coefficients. Therefore, the accuracy of the conversion coefficients gives influence to the derived electrocardiograph of the subject and the diagnostic accuracy of heart diseases. Average values of conversion coefficients (hereinafter referred to as population coefficient) acquired from an unspecified large number of persons are used as conversion coefficients. The population coefficients can guarantee some conversion accuracy statistically but cannot be regarded as optimum conversion coefficients for an individual subject. For this reason, there may occur a clinically unsatisfied difference between the derived electrocardiogram and its “true values” (values which would be obtained if they were measured).
On the other hand, it can be also considered that electrocardiographic waveforms of non-measurement portions are derived using conversion coefficients which can be applied only to a specific subject (hereinafter referred to as personal coefficients). However, there has been no specific proposal or technique like that so far.
Most of derived electrocardiograms which have been proposed so far are 12-lead electrocardiograms. In order to improve the diagnostic accuracy of heart disease of a subject who has a unique heart disease, a large number of coefficients (population or personal coefficients) which can generate a derived electrocardiogram of portions effective in the diagnosis of the unique heart disease of the subject must be prepared. However, there has been no proposal or technique for such a large number of coefficients.
Further, though it is understood to use personal coefficients specific to a subject, there has been no proposal for solving some technical themes such as how to acquire the personal coefficients, how to use the personal coefficients, and how to solve the problem that the personal coefficients of the specific subject cannot be used when the personal coefficients are absent in an electrocardiograph which is in use.